Embryology of the Reproductive Tracts Flashcards
When is the sex of an embryo determined?
At fertilization by the sperm (X or Y) that fertilizes the oocyte
When do male and female characteristics begin to develop?
The seventh week; undifferentiated from weeks 1-6
At what week do the genitalia begin to have male and female characteristics?
Week 10
At what week is the phenotypic differentiation complete?
Week 20
At the end of the 3rd week what do cells from the primitive streak form?
Paraxial mesoderm
What are the layers of the mesoderm from medial to lateral?
Paraxial mesoderm
Intermediate mesoderm
Lateral plate mesoderm
What is the mesoderm primarily responsible for?
Formation of the kidneys and internal genitalia and their ducts
Where does the urogenital ridge form?
On each side of the dorsal mesentery forming the nephrogenic and genital ridge
What gives rise to the urinary system?
The nephrogenic ridge
What gives rise to the genital system?
Genital (gonadal) ridge
What are the three slightly overlapping kidney systems formed from cranial to caudal?
Pronephros
Mesonephros
Metanephros
What do the mesonephros arise from and when?
Intermediate mesoderm
Beginning of the fourth week mesonephric tubules appear
Where do the mesonephric tubules run?
Into the longitudinal wolffian duct
What are primordial germ cells?
Spherical sex cells that are recognizable at week 5
What are the two pair of genital ducts both male and female have initially?
Wolffian (mesonephric)
Paramesonephric (Mullerian)
What do the two wolffian and Mullerian ducts come together to form?
Uterine canal
What off the Wolffian and Mullerian ducts remain in each sex?
Wolffian: male
Mullerian: female
What do the indifferent gonads consist of?
External cortex (mesothelial cells with primordial germ cell) Internal medulla
What are the primitive sex cords?
When the mesothelium of the genital ridge proliferates and cells penetrate the underlying mesenchyme in the medulla (mesothelial cells dive into the cortex)
At what week are the two sexes still identical and called indifferent gonads?
Seventh week
What does male phenotype develop?
Seventh week
What gene is needed for males to become males?
SRY gene on the short arm of the Y chromosome
What does SRY gene code for?
Testis-determining factor (TDF)
Under influence of TDF what do primitive sex cords in the medulla become?
Differentiate into seminiferous tubules
What does SRY activate aside from TDF?
Sox-9 gene a testis-specific enhancer
Inhibits Wnt4
What does Wnt4 do?
Wnt4 inhibits Sox-9
What does the absence of a Y chromosome result in?
Default formation of ovaries
What does development of female phenotype require?
Two X chromosomes
When does ovarian development begin?
12th week of development
What gene is needed for female development?
Wnt4
What does Wnt4 gene do?
Inhibits Sox-9
Activates Dax1
What do Sox-9 and Dax1 work on?
Genital ridge to form testis and ovaries respectively
What occurs to the medulla and cortex in males?
Medulla develops
Cortex degenerates
What occurs to the medulla and cortex in females?
Medulla degenerates
Cortex develops
In males, what do the mesonephric ducts give rise to?
Tubules of the rete testis and efferent ducts
In the fourth month of male development what do the primitive sex cords give rise to?
Sertoli cells
What do the Sertoli cells secrete?
AMH (anti-Mullerian hormone)
What occurs to seminiferous cords?
They remain solid until puberty then become seminiferous tubules
What forms the ovarian medulla?
Primitive sex cords dissociate into irregular cell clusters, later disappear and are replaced by vascular stroma
What are cortical cords?
Second generation of cords that proliferate in the seventh week from mesothelium
Where are mesothelium cells found?
In the cortex of the genital ridge (inside is the mesenchyme)
What do the cortical cords do?
Penetrate the underlying mesenchyme
What do the cortical cords become?
Differentiate into follicular cells wrapping around a primordial germ cell (primordial follicle)
Why do the testis descend?
Due to the disproportionate growth of the upper abdominal region away from the pelvic region
What is the gubernaculum?
Band of fibrous tissue along the posterior wall that extends from the caudal pole of the testes to the scrotum
What do the remnants of the gubernaculum serve of as an adult?
Anchor the testes within the scrotum
What does the peritoneum alongside the gubernaculum form?
Processus vaginalis
What exactly is the processus vaginalis?
The out pouching of the peritoneum or the trail the testes leave behind as they descend until it closes
At the distal end, the processus vaginalis remains, what is it called?
Tunica vaginalis of the testes
What is failure of the testes to descend called?
Bilateral undescended testes (cryptorchidism)
What is failure of the processus vaginalis to close called?
Hydrocele of the testes
What occurs if the deep ring is too loose?
Congenital inguinal hernia
What converts testosterone to DHT?
5-alpha reductase
What do testosterone receptor complexes mediate?
Virilization of the mesonephric ducts to form vas deferens, seminal vesicles, efferent ductules, and epididymis
What do DHT receptor complexes modulate?
Differentiation of the male external genitalia
What does estrogen from the mother do to females?
Stimulates (Mullerian) Paramesonephric ducts to from uterine tubes, uterus, cervix, and upper 1/3 vagina
What do the Mullerian and Wolffian ducts form together?
Uterovaginal primordium initially when they are still separate and then fuse to form uterine canal
What forms the Uterovaginal primordium (uterine canal)?
Two distal parts of the Paramesonephric ducts (Mullerian)
What separates the Uterovaginal primordium?
Uterine septum
What does the Uterovaginal primordium give rise to?
Upper 1/3 of the vagina
Fundus
Body
Cervix of the uterus
What forms the lower 2/3 of the vagina?
Sinovaginal bulbs proliferate and form a solid vaginal plate
What are the vaginal fornices?
Proximal 1/3 of vagina around the end of the uterus and of paramesonephric origin
What is the lower 2/3 of the vagina derived from?
Urogenital sinus
What are the POTENTIAL remnants of the wolffian duct in females called? (from closest to the ovaries to further away respectively)
Epoophoron
Paroophoron
What may a epoophoron form later in life?
May form Gartner’s duct and cyst
What does the mesonephric duct form in males?
Tail of epididymis, seminal vesicle, ductus deferens
What is the role of AMH?
Released from Sertoli cells and causes paramesonephric ducts in males to degenerate except for a small portion at their cranial ends forming the appendix testis
What forms on either side of the urethral fold?
Labioscrotal swellings
What determines development of external genitalia in males?
DHT
What forms the corpora cavernosa and spongiosum in males?
Genital tubercle now called the primordial phallus
What determines development of external genitalia in females?
Estrogen
What does the primordial phallus cause in males?
Pulls the urethral folds toward each other so that they form the urethral groove
What occurs in female to form external genitalia?
Genital tubercle elongates to form clit and bulb of vestibule
What occurs to urethral folds in females?
Do not fuse but form the labia minora; labrioscrotal swellings enlarge to for labia majora
What does the urogenital groove form in females?
Stays open and forms the vestibule
What is failure of urethral folds to close called?
Hypospadias
In males what do the urethral folds do?
Close to form penile urethra (urethral groove is before it closes)
What does the gubernaculum become in females?
Ovarian ligament
Round ligament of uterus
Where do gonads arise from?
Intermediate mesoderm
